I made this site about a year ago with some help from the Sitepoint users (ip Stomme Poes). The site looks great, allthough there were some issues getting it good crossbrowser. The site looks absolutely fine on ie, safari, chrome and firefox. I get however remarks from other people saying the doesn't display all that great on mobile devices and tabs. I'm currently fixing the header issues, but overall, CAN this site be better designed for ipads and stuff? With the design and css it is done now, can we change anything to make it more smartphone-friendly?Or is this the best we can get it?This is something which disturbs me a lot, can we make basic websites with a few adjustments smartphone-friendly? Or should we rewrite the whole design? CSS?

Yes, it is possible, but you will need more CSS. There is something called media queries and responsive web design. You can google that, there are lots of examples on the internet on how to implement it. You basically need difference size resources and layout for smart phones, then with the techniques I mentioned earlier, it will load the correct resources.

Good news. Your site looks like a very good candidate for adapting to mobile. However, you'll need to redesign from scratch, I believe. I suggest you look at Zurb Foundation and see what it can do for you. Foundation will supply the building blocks so your site will resize for different screen sizes.